We propose a case-control study to test the hypothesis that previous exposure to diagnostic dental X-rays and to other forms of radiation are causally related to tumors of the parotid gland. We will also evaluate the importance of other potential risk factors for this disease. Cases include all types of parotid neoplasms (both benign and malignant) identified by the LAC/USC Cancer Surveillance Program over a five year period. A neighbor control of like sex, race and age (birth year within five years) will be selected for each case. Information on dental and medical X-rays, job exposures, family cancers and tobacco and alcohol use will be obtained through telephone interviews using a standard questionnaire. Interview information on dental X-rays will be validated for a subset of cases and controls by a review of dental record. The relative importance of various exposures at different ages will be evaluated. Associations of tumor occurrence with radiation exposure and with smoking history will be analyzed separately for tumors of different histologic types.